LOL, I had a similar experience with this cereal called "ancient grains" (sold in texas, tom thumb stores).
I had nuclear farts and shits like satan himself was punishing my ass. for a week I had to sleep on my stomach!
2 guesses: you are not used to fiber and you ate too much, or it's just not gonna work, in which case I might try flax seed ground up (works for me) or oatmeal.